1. Field of the Invention
The present invention relates to a semiconductor light emitting device particularly for use in a laser apparatus.
2. Description of Background Information
In known semiconductor light emitting devices using an epitaxial layer of Group III-V nitride mixed-crystal, e.g. gallium nitride (GaN), sapphire (.alpha.-Al.sub.2 O.sub.3) is used as the material of the substrate crystal.
The crystal structure of GaN is of wurtzite type while sapphire forming the substrate has a crystal structure of corundum type. Although GaN and sapphire are both in the hexagonal system, the crystal structures of these compounds are not equivalent, as sapphire has a periodicity of thirteen atomic planes, for example. Also, these two compounds are different in the lattice constant, which in turn causes a lattice mismatch as high as 14%. Such a lattice mismatch leads to difficulties in growing an epitaxial layer having good properties and a semiconductor light emitting device using such an epitaxial layer would fail to produce an effective emission of laser beam.